1. Field of the Invention
The present invention relates to a coating and developing system and a coating and developing method for coating a surface of a substrate with a liquid resist film and for processing the substrate coated with the resist film processed by an exposure process.
2. Description of the Related Art
Processes for fabricating a semiconductor device or a LCD include a process called photolithography for forming a resist pattern on a substrate. Photolithography includes a series of processes of forming a resist film by applying a liquid resist to a surface of a semiconductor wafer (hereinafter, referred to simply as “wafer”), exposing the resist film through a photomask, and developing the exposed resist film to form a desired resist pattern on the wafer.
An exposure method coats a surface of a substrate with a liquid film and exposes the surface through the liquid film (Patent document 1). This exposure method will be referred to as “immersion exposure method”. An exposure system for carrying out the immersion exposure method will be briefly described with reference to FIG. 11. An exposure device 1 is disposed above a wafer W held in a horizontal position by a holding mechanism, not shown with a gap formed between the surface of the wafer W and the exposure device 1. The exposure device 1 is provided with a lens 10 on a central part of its lower end. A pouring opening 11 through which a liquid, such as pure water, is poured onto the surface of the wafer W and a suction hole 12 for recovering the pure water poured onto the surface of the wafer W are formed around the lens 10. Pure water is poured through the pouring opening 11 onto the surface of the wafer W and the pure water poured onto the surface of the wafer W is recovered through the suction hole 12 to form a liquid film (pure water film) in the gap between the lens 10 and the surface of the wafer W. A resist film formed on the surface of the wafer W is exposed to light emitted by a light source, not shown, and traveled through the lens 10 and the liquid film to transfer a predetermined resist pattern to the resist film.
Then, as shown in FIG. 12 by way of example, the exposure device 1 is moved horizontally with the liquid film formed between the lens 10 and the surface of the wafer W to position the exposure device 1 at the next transfer area (shot area) 13 and an exposure cycle for exposing the transfer area 13 to light is repeated to transfer the predetermined circuit pattern successively to shot areas 13 in the surface of the wafer W. In FIG. 12, the shot areas 13 are exaggerated.
Studies of forming a water-repellent protective film on a surface of a wafer W have been made to make a resist film difficult to remain on the surface of the wafer when the resist film is subjected to the immersion exposure process.
If the surface of a wafer W to be subjected to an immersion exposure process is contaminated with particles, the particles disperse in a liquid film formed for immersion exposure. If a resist film formed on the surface of the wafer W is exposed to light through the liquid film containing dispersed particles, a predetermined circuit pattern cannot be transferred to the resist film development defects are caused. Therefore, studies have been made to remove particles adhering to a surface coated with a protective film of a wafer W by cleaning the surface coated with the protective film with a cleaning liquid, such as pure water, before subjecting the wafer W to an immersion exposure process.
When pure water, namely, the cleaning liquid, wets and penetrates the protective film formed on the surface of the wafer W, a crosslinking agent, namely, a component of a solvent, contained in the resist film is eluted toward the protective film, and the protective film and the resist film merge together. The penetration degree (penetration distance I) at which pure water penetrates the protective film is expressed by Expression (1), namely, Lucas-Washburn formula.I=(d·y·cos θ/2η)1/2·t  (1)where d is the diameter of capillaries in the film, y is surface tension, θ is contact angle, η is viscosity and t is time for which the liquid is in contact with the surface of the substrate.
Different wafers W having cleaned surfaces are kept for different times, respectively, before being carried into the exposure system and the contact angle θ changes with time after the protective film has been brought into contact with pure water. Therefore, the wafers W respectively having different contact angles θ are processed by immersion exposure. Once the protective film is wetted with pure water, this phenomenon occurs also after the pure water wetting the wafer has been removed. It is known from Expression (1) that pure water penetrates protective films at different degrees of penetration if the protective films of the different wafers W have different contact angles, respectively, and hence the respective properties of the resist films of the wafers W change differently. Consequently, patterns formed by development on the wafers W have lines of different widths, respectively. The same problem arises when a water-repellent protective film and a resist film are not formed on a surface of a wafer W and a water-repellent resist film is formed on the surface of the wafer W and the surface of the resist film is cleaned with a cleaning liquid.
Patent document 1: JP-A 2005-175079